Display devices produced by using liquid crystalline compounds (the term "liquid crystalline compound(s)" is used in this specification as a general term for the compounds which exhibit a liquid crystal phase and for the compounds which do not exhibit a liquid crystal phase but are useful as component of liquid crystal compositions) have widely been utilized for the display of watches, tabletop calculators, word processors, or the likes. In recent years, researches on TFT type displays having characteristics such as a high contrast and wide visual angle are extensively conducted.
For liquid crystal compositions used for TFT, physical properties such as voltage holding ratio is high, threshold voltage (Vth) is low, their alteration caused by the change of temperature is small, temperature range of liquid crystal phase is wide, miscibility with other liquid crystal materials is excellent, and viscosity is low have been sought. Further, liquid crystal compositions having a high optical anisotropy (.DELTA.n) are useful for increasing response speed.
For these purposes, fluorine containing compounds are suitable. Many researches have been conducted up to now and for example, (1) Japanese Patent Publication No. Sho 63-13411, (2) Japanese Patent Publication No. Sho 63-44132, (3) Laid-open Japanese Patent Publication No. Hei 2-233626, (4) Laid-open PCT Japanese Publication (Tokuhyo) No. Hei 2-501311, (5) Laid-open PCT Japanese Publication No. Hei 3-500413, (6) Laid-open PCT Japanese Publication No. Hei 2-501071, (7) Laid-open PCT Japanese Publication No. Hei 3-503711, (8) Laid-open Japanese Patent Publication No. Hei 4-217930, (9) Laid-open PCT Japanese Publication No. Hei 4-501575, (10) Laid-open PCT Japanese Publication No. Hei 6-504032, and (11) EP-439089 are published.
A part of the compounds of the present invention are formally included in the general formula disclosed in the publications (6) to (11) mentioned above. However, data such as physical property values of the compounds which correspond to the ones of the present invention are not disclosed at all and their specific characteristics are not specifically described in any one of the publications mentioned above. Accordingly, those publications have not suggested the present invention.